What a load of horseshit!
ElizabethGardens is working on a complete overhaul of a 1/3 acre lot, starting with bringing in a glorious load of manure and compost to improve the soil. So one question is, how much to buy? There's a great shortcut to converting square feet into inches of mulch. Just multiply the square footage of your garden by the inches of coverage you want, and divide by 324. That'll tell you how many cubic yards you need.
Let's say this 1/3 acre lot--14,370 square feet--actually has 10,000 square feet of garden space. The rest, let's say, is taken up with house, outbuildings, driveway, patio, sidewalks, paths, etc.
So maybe you want 6 inches of mulch in the garden. 10,000 square feet x 6 = 60,000. Divide by 324, and you get 185 cubic yards. That's quite a load of manure!
(Here, by the way, are links to many great agricultural-related calculators. You can also easily calculate the amount of mulch, stone, etc. you'll need for a garden project here.)
Now the question is: what do to with all this mulch? Just lay it down on top of what's there (weeds, grass, whatever), or till it in, or use some kind of weed barrier?
There's no easy answer. Plastic weed barriers aren't great for the soil ecology, weeds will spring up anyway, and eventually you'll have exposed plastic somewhere. If you just smother weeds with mulch, they'll probably find their way to the surface eventually, although new weeds will creep in thanks to wind, bird droppings, etc. anyway. Finally, the mulch you bring in could contain weed seeds, too. (the only way to know for sure is to take a sample, water it, and wait.) Tilling can disrupt a healthy soil community and drive away earthworm populations.
What would I do, given the glorious possibility of a blank slate and a load of mulch? Prioritize. Choose a manageable-sized area and just focus on that in the first year. Maybe you're eager to get a vegetable garden in before summer; maybe you'd like to get the front yard done before the neighbors circulate a petition. Do that this year, and just keep the rest mowed or seed in a cover crop like vetch, fava, rye or clover that will improve the soil and choke back weeds while it waits its turn. (Check with your nursery for the best cover crop for your climate, and discuss with them whether you should let the crop go to seed or whack it back when it starts to bloom. It's not a big deal, for instance, if fava goes to seed, but some rye cover crops could be with you forever if you let them bloom.)
Then, with this smaller, manageable area, don't bother tilling. Just pile the stuff on top. For a weed barrier consider thick, overlapping layers of wet cardboard and newspaper, which will gradually turn into worm food. (use anything but glossy magazine inserts or coated color cardboard.)
For raised beds, if you're on a budget, consider straw bales. (I'm not sure what the situation is nationwide, but rice straw is weed-free and widely available in California.) I got this idea from Seattle Tilth--the idea is to just set a straw bale, still wrapped in its string, on the ground (or perhaps bury it slightly to get it to the height you want), hollow out the center, fill it with good potting soil and compost, and plant right into it. (You can use the straw you hollowed out of the bale as mulch in your paths, or compost it.)
For easy watering, thread drip irrigation lines through the bales, and water the entire bed, bales included, with weak compost tea from time to time to encourage healthy roots. At the end of the season, throw the whole thing in the compost pile or just spread it around on the ground, pile more compost on top, and let that be next year's garden. (Mind you, I have yet to try straw bale gardening myself, although I'm dying to. Has anyone else tried it?)
Last suggestion: Whatever you're going to plant, crowd plants together. Plant 3 or 5 or 7 of the same plant in a smaller area than the directions on the plant tag recommend. You'll crowd out weeds and get a better-looking garden faster. Then, next year, when you start on another section, you can pull out a few plants that are starting to get overcrowded and move them to your new beds.
What fun! I wish I had another blank slate. That vacant lot across the street sure is looking good...
elizabethgardens: What to do...what to do...